A special scientific research team has finally published its answer to a grisly mystery. Five years ago, something drove a group of approximately 100 melon-headed whales, ordinarily a deep-ocean species, into the shallows of the Loza Lagoon system, off the Madagascar coast. Despite urgent efforts to guide the animals back to the open sea, at least 75 of the stranded whales died. Now the independent panel of five scientists has concluded that the "most plausible and likely behavioral trigger" for the incident was sonar emissions from a seafloor survey vessel.
That's bad news for ocean explorers. "This is the first known such marine mammal mass stranding event closely associated with relatively high frequency mapping sonar systems," says the panel's report, released by the International Whaling Commission. It has long been known that low-frequency sonar can cause physical trauma to whales and disrupt their diving and migratory patterns. As a result, commercial survey vessels generally use high-frequency sonar systems, which until now were considered relatively harmless to whales.
But the link in this case seems strong. On May 29, 2008, a survey vessel contracted by ExxonMobil used a 12 kHz multibeam echosounder system to map the ocean floor 40 miles off the coast of Madagascar. According to the panel's report, the sound from such a system would have been "clearly audible over many hundreds of square kilometers of melon-headed whale deepwater habitat areas." The next day, a group of melon-headed whales swam into the lagoon and could not get out. It was the first time the species had ever been spotted in these coastal shallows.
ExxonMobil rejects the report’s conclusion. "ExxonMobil believes the panel's finding about the multibeam echo sounder is unjustified due to the lack of certainty of information and observations recorded during the response efforts in 2008," company spokesman Patrick McGinn told Agence France-Presse. Malagasy government observers aboard the survey vessel saw no whales in the mapping area. Other scientists are also voicing doubts.
And a killer is out there somewhere.